A frequently used synthetic method for the preparation of unsaturated aliphatic compounds has been the Wittig coupling of an arylphosphonium ylid with an aldehyde or ketone. Suitable procedures for the preparation of ylids and the Wittig reaction are described in A. W. Johnson, "Ylid Chemistry" Academic Press, Inc., New York (1966). The method has proven to be of particular importance in the preparation of unsaturated aliphatic compounds useful as insect sex pheromones. A review describing the preparation of these attractants is "The Synthesis of Insect Sex Pheromones" by Clive A. Hendrick in Tetrahedron, Volume 33, pp. 1845-1889 (1977). Additional reports on the preparation of unsaturated alkyl compounds using phosphonium ylids can be found in U.S. Pat. Nos. 3,712,880; 3,732,282; and 3,671,558.
More specifically, the sex pheromone of the female pink bollworm moth has been identified as a mixture of the 7Z,11Z)- and (7Z,11E)-7,11-hexadecadien-1-yl acetate, Hummel, et al., Science, 181, 873 (Aug. 31, 1973). A number of syntheses of this pheromone and related compounds have also been described by Anderson and Hendrick in U.S. Pat. Nos. 3,919,329; 3,953,532; 3,987,073; and 3,989,729, and by Sonnet, in the Journal of Organic Chemistry, 30, pp. 3793-3794 (1974).
A disadvantage of these described procedures is that the phosphonium ylid used for the coupling normally is used to introduce only one double bond thus necessitating a number of additional chemical reactions, reagents, solvents and so forth to introduce additional double bonds into the aliphatic carbon chain. It has been further found that previously described methods suffer from a number of inherent disadvantages, including multiple reaction steps which lead to poor results for large-scale preparations.
It would therefore be extremely valuable to have a process for preparing unsaturated aliphatic compounds utilizing a single cyclic phosphonium ylid by reaction with a suitable carbonyl derivatives to afford the desired unsaturated aliphatic compounds easily and in high yield and purity, and that is also readily adaptable to large-scale commercial production.